This research project deals with the role of the intestine in the regulation of sterol and bile acid metabolism. Specifically, it is proposed to investigate: 1) The relationship between intestinal sterol biosynthesis, the degradation of sterols and bile acids by intestinal microorganisms and the cholesterol/bile acid balance of the intact organism. 2) The formation of C-25 hydroxylated intermediates during cholic acid biosynthesis and the effect of the polyhydroxylated bile alcohols on the activities of the intestinal bacteria and on cholesterol/bile acid balance.